In a stringed instrument it is often desirable to change the tone of sound produced by a vibrating string while the string is vibrating. This effect may be accomplished by sliding fingers or a steel bar down the string or by changing the tension on the string while it is vibrating. In known prior art devices, lever mechanisms have been placed on or in a stringed instrument connected to the strings for facilitating the operation of changing the tension on one or more strings.
For example, U.S. Pat. Nos. 1,864,690 to Guibeaud; 2,201,536 to Harvey; 2,949,806 to Turman; 3,721,150 to Hoffman; and 3,479,917 to Zitnik disclose lever mechanisms mounted on the front face or neck of a guitar or other stringed instrument for varying the tension of the instrument strings. U.S. Pat. Nos. 3,512,443 to Parson, et al., and 3,686,993 to Fender disclose lever mechanisms mounted inside a guitar, usually on the rear side thereof. The Parson and Fender mechanisms have levers designed for attachment to the shoulder strap normally used to support the guitar on a performer's neck. The lever is actuated by forcing the guitar downwardly so that the shoulder strap pulls the lever and tensions at least one guitar string.
These prior devices are generally bulky and inconvenient to operate. The levers mounted on the face or neck of the guitar detract from the appearance of the guitar, and some of the devices require a free hand to operate the levers. Often, a performer will not have a free hand when he desires to change the tone of a particular string.
The shoulder strap operated levers require two or three inches of instrument movement to accomplish less than one-eighth of an inch movement in the instrument string. Because of the bulk of these shoulder strap type devices, they are expensive to manufacture and install in a guitar, and it would require a major butchering of an instrument to retrofit these devices into an existing instrument. Thus, it would be totally impractical to retrofit a valuable guitar or other stringed instrument with these known prior art devices.
Many prior art devices, such as the shoulder strap operated lever mechanisms, are designed to act upon one string or one group of strings and are, thus, limited in their versatility and usefulness. Also, such prior art devices generally do not provide a convenient mechanism for deactivating the entire device when desired so that tone changes are not accidentally created.